题目

A degree can be a valuable virtue for increasing your income. However, the job market for the highest paying jobs is also extremely competitive. If you are a new member into those job markets, without job experience to match your education, a degree will not help you get a job. Fortunately, the majority of job openings in 2013 do not require a degree. This includes many of the most reliable employment opportunities in the fastest growing fields. Degrees are not required to work as a personal care assistant or home health assistant, both among the fastest growing occupations in the US t若函数f(x)有反函数,则方程f(x)=a(a∈R)(    )A.有且仅有一个实根                   B.至多有一个实根C.至少有一个实根                     D.没有实根